The present invention relates to vacuum tubes, and more particularly to a minute evacuated device employing thin film electrodes suitable for use in high temperature, high radiation, and high vibration environments that preclude the employment of conventional vacuum tubes or semiconductor devices. Ceramic and metal construction vacuum tubes have been employed in the past for this purpose, but their excessive size, weight, and power consumption prevent extensive employment, as in circuits requiring a great number of such devices such as computers or severe environment instrumentation.
Integrated vacuum tube structures have been proposed in the past. Exemplary of the prior art is U.S. Pat. No. 3,978,364 issued Aug. 31, 1976 to J. Dimeff et al. Such devices are known as integrated thermionic circuits, and utilize integrated circuit photodeposition processes in conjunction with vacuum tube techniques, producing a microminiature vacuum tube. In these devices there are no separate grid structures in the form of a screen as in conventional vacuum tubes. The grid, cathode, and anode are all fabricated of thin films sputtered onto an insulating substrate and then delineated by standard photolithographic techniques. These devices can withstand temperatures in excess of 500.degree. C. with high packaging densities. Furthermore, these devices are extremely radiation resistant, allowing application thereof in high radiation environments. However, in these prior art devices, the emitted electrons obtain such large momenta within the first few microns after emission that, instead of traveling nearly perpendicular to the equipotential lines, many are not turned to travel to the anode, but "spray" in all directions.